1. Field of the Invention
The present invention relates to a lensbarrel, and more particularly to a lens barrel which performs focus adjustment, variable power and the like by moving a lens group in an optical axis direction in a projector, a camera and the like.
2. Description of the Related Art
In the projector, the camera and the like, as a moving system for moving the lens group in an optical axis direction for focus adjustment and variable power, there is known a helicoidal system using a helicoidal screw. The helicoidal system is a system in which an inner barrel body for holding a lens, and an outer barrel body for being rotationally driven are threadedly engaged and coupled by means of a helicoidal screw, and the inner barrel body is moved along an optical axis by means of a feeding operation of the helicoidal screw by rotating the outer barrel body:
In the case of the helicoidal system, it is not easy to manufacture helicoidal screws such that male and female helicoidal screws are caused to be threadedly engaged without looseness, but for example, when there occurs looseness in a thrust direction, a so-called backlash occurs to cause a position of the lens to be shifted. When molding is performed with little clearance between the male and female helicoidal screws in order to cope with such looseness, there is a problem that in addition to torque of rotation increased due to an increase in friction, it takes a great deal of time to adjust a die during molding of the helicoidal screws.
Conventionally, there has been a lens barrel (See Japanese Patent Application Publication No. 57-210304), in which a spring piece for pressing is provided at a male helicoidal screw portion of the inner barrel body, and this spring piece is thrusted against a thread of the female helicoidal screw of the outer barrel body, whereby looseness which occurs on the helicoidal screw is eliminated.
Also, there has been a lens barrel (See Japanese Patent Application Publication No. 8-304688), in which the outer barrel body is divided and arranged in a thrust direction and each of the outer barrel bodies obtained by the division is coupled through a coupling member having an elastic force in a thrust direction. Thereby, a biasing force in the thrust direction is imparted to the outer barrel bodies thus divided to each other, and this biasing force brings the male helicoidal screw to intimate contact with the female helicoidal screw to make it possible to eliminate looseness of the helicoidal screw in the thrust direction. Further, since this coupling member is provided with a spring piece, and this spring piece is thrusted against the thread of the male helicoidal screw of the inner barrel body, looseness of the helicoidal screw in the radial direction can be also eliminated.
The lens barrel described in the Japanese Patent Application Publication No. 57-210304 has, however, had a disadvantage that the biasing force of the spring piece wears the thread of the female helicoidal screw early. Also, the lens barrel described in Japanese Patent Application Publication No. 8-304688 has had a disadvantage that the torque of rotation is increased due to high friction on the screw surface in addition to an increased number of components.